Generally, aromatic hydrocarbons are obtained by separating feedstocks, having large amounts of aromatic compounds, such as reformate produced through a catalytic reforming process and pyrolysis gasoline produced through a naphtha cracking process, from non-aromatic hydrocarbons through solvent extraction. The aromatic hydrocarbon mixture thus separated is typically separated into benzene, toluene, xylene and C9+ aromatic compounds depending on differences in boiling point, and thus is used as a fundamental material in the field of the petrochemical industry. On the other hand, the non-aromatic hydrocarbons are used as raw material or fuel of the naphtha cracking process.
In this regard, U.S. Pat. No. 4,058,454 discloses a solvent extraction process for separating and recovering polar hydrocarbons from a hydrocarbon mixture including polar hydrocarbons and nonpolar hydrocarbons. In the solvent extraction process known in the art including the above patent, the nature in which the aromatic hydrocarbons are polar in common is used. That is, when a solvent, capable of dissolving a polar material, such as sulfolane, contacts the hydrocarbon mixture, polar aromatic hydrocarbons are selectively dissolved and thus separated from the nonpolar non-aromatic hydrocarbons. This method is advantageous because a highly pure aromatic hydrocarbon mixture can be obtained, but suffers because additional solvent extraction equipment is required and the solvent should be continuously supplied during the process. Thus, the development of methods of separately obtaining aromatic hydrocarbons and non-aromatic hydrocarbons from feedstock even without an additional solvent extraction process has been required.
In order to separate the aromatic compound from the non-aromatic compound, attempts have been made using a reaction system other than the solvent extraction process. The non-aromatic compound, mixed with the aromatic compound, is converted into gaseous hydrocarbon through hydrocracking in the presence of a catalyst, and the aromatic mixture and the non-aromatic mixture are separated from each other using a gas-liquid separator positioned at an end of a reactor. Such a concept has been developed in U.S. Pat. No. 3,729,409. Further, U.S. Pat. Nos. 3,729,409, 2,849,290, and 3,950,241, aim to be a method of producing a high-quality gasoline component by converting a linear hydrocarbon component mixed with an aromatic compound into a gaseous component through hydrocracking using ZSM-5 zeolite to increase the amount of aromatic component in a liquid component. Such a concept has been developed for a process of increasing production of benzene/toluene through a reforming process by filling parts of continuous reactors for a reforming process with a zeolite catalyst, as disclosed in U.S. Pat. No. 5,865,986. In addition, U.S. Pat. No. 6,001,241 discloses a method of increasing a yield of aromatic component by filling parts of reactors for a reforming process with a zeolite catalyst having similar reaction properties. However, the above concept has not yet been applied as an independent process separate from a reforming process for producing an aromatic component. In the case where the feedstock including reformate and pyrolysis gasoline is treated as an independent process, LPG may be further produced along with the aromatic component. In particular, in regions where almost all of the LPGs depend on importation, as in Korea, if LPG were produced as a by-product, it may substitute for a considerable amount of imported LPG.
However, the commercially available application of the above concept is under many restrictions. In particular, the deposition of coke on a catalyst may be caused by a side reaction, thus shortening the lifetime of the catalyst. Hence, techniques for overcoming this problem are required. The deposition of coke may be suppressed by supporting a metal component having high hydrogenation activity, such as metals corresponding to a Group VIII of the periodic table, onto a zeolite catalyst. However, the high hydrogenation activity of the metal component entails a side reaction converting the aromatic compound into the non-aromatic compound through a hydrogenation reaction. Thus, there is need for controlling the hydrogenation function by the metal component. In U.S. Pat. No. 5,865,986, the content in which metal activity is controlled using a sulfur compound is incorporated. Accordingly, research into methods of controlling the hydrogenation activity of a metal of a Group VIII by introducing another metal component has been continuously conducted.